I read in some posts(post1 and post2) that aria-hidden="true" hides the element from all user agents.  
aria-hidden (state): Indicates that the element and all of its descendants are not visible or perceivable to any user as implemented by the author.
- Does 
aria-hidden="true"hides the element from all user agents or only screen-readers? - If yes, then in bootstrap why is the glyphicon inside the 
carousel-controlicon visible even with the attributearia-hedden="true"?